In an ignition system that ignites an air-fuel mixture in a cylinder of an internal combustion engine, a system configured to perform so-called multiple-discharge in order to improve a combustion condition of the air-fuel mixture is known.
For example, a configuration that produces a plurality of discharges intermittently in one combustion stroke is disclosed in Patent Document 1.
On the other hand, a configuration that connects two ignition coils in parallel in order to obtain long multiple-discharge characteristics of the discharge time is disclosed in Patent Document 2.
Furthermore, an ignition system for an internal combustion engine for controlling a second switch means to be repeatedly turned on/off to provide an inversion of positive and negative current to a spark plug so that a stable predetermined output current flows even when a voltage of a power supply connected to an energy storage coil is varied is disclosed in Patent Document 3. The control includes a period where energy stored in the energy storage coil is increased sharply by turning a first switching means on during a period that the second switching means is turned off, and a period where the energy stored in the energy storage coil is increased gradually by turning a fourth switch means on during the period that the second switching means is turned off.